1921] The Chemical Behavior of Zirconium 117 



water, losing one molecule of water and changing to zirconyl hydroxide. 

 It is more easily soluble in acids than zirconyl hydroxide. At various 

 stages in the hydrolysis the addition of ammonium hydroxide will 

 give precipitates of different composition These have been con- 

 sidered by some as new hydroxides, but there is little proof that they 

 are not mere mixtures. It has been suggested that there are two 

 hydroxides with the formula ZrO(OH)2, ordinary zirconyl hydroxide, 

 which is amphoteric, and a metazirconic acid. No salts of the latter 

 are definitely known and its existence has been disputed. 



While in all cases the hydrolysis is progressive, it is almost certain 

 that all the molecules do not react with water at the same time, and 

 hence at any one time various stages of hydrolysis may be present 

 in a solution. It is common, however, for one of the stages to pre- 

 ponderate. It may therefore be possible to observe definite steps in 

 the progression when there are formed basic zirconyl compounds 

 which either separate by precipitation because of their insolubility 

 or by crystallizing with molecules of water, forming difficultly-sol- 

 uble salts, or otherwise afford indications of their presence through 

 physical tests such as electrical conductivity, thermo-chemical data, 

 cryoscopic determinations, etc. One of the most frequently occuring 

 of these basic compounds is Zr 2030)2, known as Endemann's chloride. 

 Its analogues are Zr203.S04, Zr203(N03)2, Zr203(SCN)2, and others. 

 These have always been obtained in the hydrated condition, and it 

 has been observed that the last portion of the water is removed with 

 considerably greater difficulty. This fact, combined with that of 

 leaving the colloidal hydroxide on dialysis, leads to the suggestion 

 that the formulas be written ZrO(OH)2.ZrOCl2, ZrO(OH)2.ZrOS04, 

 etc. These indicate the degree and order of the hydrolysis. Thus 

 the steps are ZrCl4+H20= ZrOCl2+2HCl; 2ZrOCl2+H20= ZrO 

 (OH)2.ZrOCl2+2HCl. In the first stage all of the tetrachloride is 

 hydrolyzed. In the second, one-half of the zirconyl chloride is hy- 

 drolyzed and the colloidal hydroxide formed either combines chemi- 

 cally with the zirconyl chloride or forms an adsorption compound 

 with it. It is difficult in this and a number of similar cases to con- 

 ceive of these substances where the composition is definite and the 

 conditions of formation are accurately known as other than definite 

 chemical compounds. Thus at a temperature of 39.5° between the 

 dilutions 1: 4 and 1: 120 the sulphate Zr(S04)2 is hydrolyzed with 

 the production of a crystalline substance having the composition 

 4Zr02.3S04.14H20, which may also be written ZrO(OH)2.3ZrO. 



